1. Field of the Invention
The present invention relates to a body supporting apparatus such as a chair, a sofa, a bed and a stretcher. In this specification, the word "body" means both a body of a human being and a body of an animal.
2. Description of the Related Art
A typical example of body supporting apparatus is a chair. The commonest technique used for giving a soft, comfortable touch to a chair's seat and seat back is to attach a thick cushion made of a sponge or urethane foam to the base plates of the chair's seat and the seat back.
In order to produce a chair which is comfortable to sit on, it is necessary to support the weight of a body uniformly by a large area of the seat and the seat back. In other words, the body should be prevented from being pressed only at particular points.
In this regard, a cushion tends to be easily flattened while being repeatedly compressed in use. The thus flattened cushion cannot properly disperse the weight of the body, thereby failing to provide an appropriate weight-supporting function.
In view of this, various methods have been proposed to improve the weight-supporting function of a chair. For instance, Japanese Utility Model Application Laid-open No. 4-118059 discloses an improved arrangement of a seat back. Specifically, it teaches that an outer member constituting a rear side portion of the seat back can be made of a flexible synthetic resin material. With such an arrangement, when a person leans on the seat back, the outer member is deformed elastically, thereby allowing the seat back to incline backward.
Generally, for providing an excellent rocking performance, it is necessary to utilize a large area of the seat back in order to equally support the load applied by the upper part of a person's body. To this end, particular portions of the seat back which support a greater pressure applied by the person's body should be arranged to deform to a greater extent than the other portions of the seat back. In other words, the seat back needs to be deformed suitably to fit the person's body. However, according to the arrangements disclosed in Japanese Utility Model Application Laid-open No. 4-118059, the rocking function of the seat back is provided only by the elastic deformation of the outer member while the seat back itself fails to perform appropriate deformation to fit the person's body.
Japanese Patent Application Laid-open No. 9-182643 teaches that a base member of a seat and a base member of a seat back are both hollow. Peripheral walls of these bodies are arranged to have a bellows-like configuration. In such an arrangement, weight-supporting function is provided by utilizing the elastic deformation of the bellows-like peripheral walls.
According to the arrangements disclosed in Japanese Patent Application Laid-open No. 9-182643, it is possible to obtain a better weight-supporting performance than by the arrangements of Japanese Utility Model Application Laid-open No. 4-118059. However, the former arrangements are disadvantageous in that the hollow bodies are difficult to precisely make from a synthetic resin material.
According to another example of prior art applied to a chair or a bed, use is made of a cloth which is spanned on a metal frame. However, a cloth tends to lengthen while being repeatedly used. Thus, a cloth is not used for a chair required to have durability.
According to still another example of prior art applied to a chair's seat, use is made of a seat supporting member having a net-like configuration. This seat supporting member, which is made of a synthetic resin by injection molding, is fixed to a frame and covered with a cushion. Such an arrangement is similar to that of a hammock, and the thus arranged seat supporting member tends to be excessively deformed, thereby failing to stably support the person's body. Thus, the above arrangement is not necessarily suitable for a chair to be used in an office for a long period of time.